There has been known, as a conventional microstructural member to be produced using a technology of micro-electro-mechanical systems (MEMS) or the like, a structural member which is divided into a plurality of regions electrically insulated from each other and which is used as an electrode so as to perform driving, control, and detection of a displacement and the like by using electrical signals, with respect to a structural member and a movable member. With such a structure, an actuator having a plurality of driving force generating mechanisms, a sensor having a plurality of electrostatic detection portions, and the like can be easily achieved. Specific examples thereof will be described below.
Japanese Patent Application Laid-Open No. 2000-065855 discloses a semiconductor acceleration switch of a structure in which an insulator is provided between a plurality of movable electrodes to be used as beam portions. FIG. 13 is a perspective view of the acceleration switch disclosed in Japanese Patent Application Laid-Open No. 2000-065855. In FIG. 13, the acceleration switch includes a support substrate 901, a fixed portion 902, a movable portion 903, a fixed electrode 905, a control electrode 906, and stoppers 907a and 907b. Further, the acceleration switch includes a supporting portion 908, beams 909, 991, and 992, a mass member 910, movable electrodes 911 and 913, a frame portion 916, an insulating film 917, a movable portion main body 930, terminals 981 and 982, and an electrode 961. In such structure, the insulating film 917 is formed between the movable electrodes 911 and 913, thereby forming the beam 909. By the beam 909, the mass member 910 which is applied with an acceleration to be input is held. The plurality of movable electrodes 911 and 913 included in the beam 909 are insulated from each other, and sensor characteristics are controlled between the movable electrode 911 and the fixed electrode 902, whereby the acceleration can be detected between the movable electrode 913 and the fixed electrode 905. In the structure disclosed in Japanese Patent Application Laid-Open No. 2000-065855, in each of deep and narrow trenches formed in the silicon substrate, the insulating film 917 such as a spin-on-glass (SOG), a thermally oxidized film, or a polysilicon is formed.
Further, Japanese Patent Application Laid-Open No. 2000-286430 discloses a semiconductor dynamic quantity sensor having a structure in which insulating films are embedded in a supporting portion for beams and in a supporting portion for electrostatic comb teeth so as to be insulated from other portions. FIG. 14 is a perspective view of the semiconductor dynamic quantity sensor disclosed in Japanese Patent Application Laid-Open No. 2000-286430. As illustrated in FIG. 14, the semiconductor dynamic quantity sensor includes a single crystal silicon substrate 1, trenches 4a to 4d, a square frame portion 5, a beam structural member 6, anchor portions 7 and 8, beam portions 9 and 10, a mass portion 11, movable electrodes 12a to 12d, movable electrodes 13a to 13d, trenches 14a and 14b, insulating materials 15a to 15d. In addition, the semiconductor dynamic quantity sensor includes first fixed electrodes 16a to 16d, second fixed electrodes 17a to 17d, trenches 18a to 18d, insulating materials 19a to 19d, trenches 20a to 20d, insulating materials 21a to 21d, first fixed electrodes 22a to 22d, second fixed electrodes 23a to 23d, trenches 24a to 24d, insulating materials 25a to 25d, trenches 26a to 26d, and insulating materials 27a to 27d. 
The beams 9 and 10 which support the mass portion 11 are held by the square frame portion 5 through the insulating materials 15a to 15d. On the other hand, the first fixed electrodes 16a to 16d and 22a to 22d and the second fixed electrodes 17a to 17d and 23a to 23d are held by the square frame portion 5 through the insulating materials 19a to 19d, 21a to 21d, 25a to 25d, and 27a to 27d. With the structure, the square frame portion 5, the mass portion 11 including the movable electrodes 12a to 12d and 13a to 13d, the first fixed electrodes and the second fixed electrodes are electrically insulated from each other and are mechanically held. As a result, owing to a dynamic quantity of an object to be measured, the mass portion 11 can be moved. An electrostatic capacitance between the first fixed electrode and the first movable electrode, and an electrostatic capacitance between the second fixed electrodes and the second movable electrodes are detected, whereby a movable amount thereof can be detected.
Japanese Patent Application Laid-Open No. 2000-286430 discloses a technology in which a silicon oxide film is formed in the interior of the formed trenches and a polysilicon film is further formed to be embedded in each of the trenches. In the document, there is a description that the combined use of polysilicon of low stress produces an effect of reducing the stress generated in the trenches as compared with the case where only the single silicon oxide film is embedded in the trenches.